Optical fiber is now used in a variety of telecommunication applications because of its small physical size and high bandwidth capacity.
An optical fiber access network provides for the distribution of telecommunications data among various locations, such as between a central office (CO) and a location remote from the CO, often called an optical network unit (ONU), over optical fibers.
In many current optical access networks, the active components in the CO, which include optical and electrical devices, are powered by the power that a power utility supplies directly to the building or facility housing the CO. The ONU likewise requires electrical power for converting optical signals to electrical signals for further processing and distribution and for converting electrical signals to optical signals for transmission back through the fiber network to the CO. This power can originate from the same source in the CO, or more often, originate from a power source located remotely from the CO. This remote power source (RPS) typically converts AC power supplied by the power utility to a lower voltage DC power suitable for handling by communications craftspersons.
The most common method of carrying the power from the CO or RPS to the ONU is via a standard copper twisted-pair telephone cable or a standard coaxial cable, neither of which contains optical fiber. In addition, it has been proposed to carry the power by using a composite cable including groups of twisted-pair telephone wires bundled together in some fashion with a plastic tube or tubes containing optical fibers. See U.S. Pat. No. 5,268,971, incorporated by reference herein.
These composite cables, however, are unsatisfactory in terms of their size, scalability, maneuverability and taut-sheath accessibility. Conventional composite cables which contain electrical conductors arranged as twisted pairs or bundles have a large diameter and are heavy in weight. These conventional cables are of such size and weight because two wires which are twisted as opposed to untwisted or wires which are grouped as opposed to layered require excess space. The space requirement of the electrical conductor portion of these composite cables typically constitutes the greatest proportion of the composite cable. The contribution of the electrical conductors to the size of the composite cable limits the scalability of the cable design in terms of the number of optical fibers and electrical conductors which can be included during cable manufacture, because the size of the cables utilized in optical fiber networks must satisfy preset standards as to duct sizes, splice enclosures entrance ports, installation equipment and termination hardware. Also, a composite cable which is heavy and has a large diameter is extremely bulky and, thus, hard to maneuver in storage and installation. In addition, conventional composite cables are not constructed to allow for ease of mid-span or taut-sheath access to the optical fibers without damage to the electrical conductors when the electrical conductors surround the optical fibers in the composite cable.
Furthermore, the need for twisting the telephone wires when they are used for power distribution is disappearing in modern fiber access networks because of an increased confidence in the reliability of the fiber network as the only communications medium and a decreased interest in having communication-grade twisted-pairs available for future use.
Therefore, there exists a need for a composite cable which is compact, has a small diameter, is lightweight, mechanically protects the optical fibers from damage, is scalable in terms of optical fiber and electrical conductor capacity, is easy to install and terminate, allows for ease of mid-span or taut-sheath fiber access without harm to either the fibers or the conductors and is compatible with modern optical access network limitations and standards.